Quick measurement of NMR-coil sensitivity with a dual-loop probe

Abstract

The radio-frequency coil sensitivity for NMR signal detection can be defined as B1/√P, which is the magnetic field that the coil induces at a given point per unit supplied power. We propose a new method, based on the reciprocity theorem, to quickly evaluate the sensitivity of a tuned coil. The only requirement of the method is a voltage gain measurement with a small dual-loop probe, without mobilization of the NMR unit. The probe can be used to gauge and map the sensitivity of the coil with good accuracy, while monitoring its tuning frequency ω0 and its quality factor Q. Our method is particularly convenient for development and maintenance of coils for MR imaging, and more generally could be applied to other fields involving radio-frequency characterization of inductive circuits.